POPULATION STRUCTURE AND LEVELS OF GENE FLOW IN THE MEDITERRANEAN LAND SNAIL ALBINARIA CORRUGATA (PULMONATA: CLAUSILIIDAE)

The amount of gene flow among local populations partly determines the relative importance of genetic drift and natural selection in the differentiation of such populations. Land snails, because of their limited powers for dispersal, may be particularly likely to show such differentiation. In this study, we directly estimate gene flow in Albinaria corrugata, a sedentary, rock-dwelling gastropod from Crete, by mark-recapture studies. In the same area, 23 samples were taken and studied electrophoretically for six polymorphic enzyme loci. The field studies indicate that the population structure corresponds closely to the stepping-stone model: demes are present on limestone boulders that are a few meters apart, and dispersal takes place mainly between adjacent demes. Average deme size (N) is estimated at 29 breeding individuals and the proportion of migrants per generation at 0.195 (Nm = 5.7). We find no reason to assume long-distance dispersal, apart from dispersal along occasional stretches of suitable habitat. Genetic subdivision of the population, as derived from F_ST values, corresponds to the direct estimate only at the lowest spatial level (distance between sample sites < 10 m), where values for Nm of 5.4 and 17.6 were obtained. In contrast, at the larger spatial scales, F_ST values give gene-flow estimates that are incompatible with the expected amount of gene flow at these scales. We explain these discrepancies by arguing that gene flow is in fact extremely limited, making correct estimates of Nm from F_ST impossible at the larger spatial scales. In view of these low levels of gene flow, it is concluded that both genetic drift and natural selection may play important roles in the genetic differentiation of this species, even at the lowest spatial scales.     

Historic and recent fragmentation coupled with altitude affect the genetic population structure of one of the world's highest tropical tree line species

Aim To assess the effects of altitude and historic and recent forest fragmentation on the genetic diversity and structure of the wind‐pollinated tropical tree line species Polylepis incana. Location One of the highest mountain forest regions of the world, located in the Eastern Cordillera of the Ecuadorian Andes. Methods We compared genetic diversity and structure of adult trees with those of seedlings (n= 118 in both cases) in nine forest stands spanning an altitudinal gradient from 3500 to 4100 m a.s.l. using amplified fragment length polymorphisms (AFLPs). Genetic diversity was calculated as percentage of polymorphic bands (P) and Nei's expected heterozygosity (He); genetic differentiation was assessed using analysis of molecular variance, Φ_ST statistics and Bayesian cluster analysis. Results Estimates of genetic diversity at the population level were significantly lower in seedlings than in adults. Genetic diversity (He‐value) was, in both cases, negatively correlated to altitude and positively correlated to population size in the seedlings. Genetic differentiation of the seedlings was approximately as high (φ_ST= 0.298) as that of the adults (φ_ST= 0.307), and geographical differentiation was clearly reflected in both AFLP profiles, with mountain ridges acting as barriers to gene flow. Main conclusions Our study provides evidence of a historic upslope migration of P. incana in central Ecuador. In addition, it highlights the detrimental effects of unexpectedly strong genetic isolation, both recent and historical, particularly for our wind‐pollinated species where the distance between forest stands was less than 25 km. We therefore additionally propose that in habitats with pronounced high‐mountain landscape structures, gene flow may be hampered to such an extent that species have a more pronounced sensitivity to habitat fragmentation, even among populations of wind‐pollinated trees.     

INDIRECT METHODS TO ESTIMATE GENE FLOW IN CAVE AND SURFACE POPULATIONS OF ANDRONISCUS DENTIGER (ISOPODA: ONISCIDEA)

We estimateci gene flow among several populations of the troglophilic woodlouse Androniscus dentiger from central Italy using allozyme data. Estimates of gene flow were obtained from G_ST, θ, and the private alleles method, after being tested whether the assumption of the population genetic model and the assumption of neutrality of alleles had been met. Hierarchical analysis of gene flow has been used to investigate the geographic scale at which gene exchange can actually occur. Results showed that, independent of the methods, no ongoing gene flow can be detected among populations, even among geographically proximate ones. Genetic drift is likely the main agent shaping the pattern of genetic divergence among these populations. Patterns of past and ongoing gene flow were considered, as surface populations have become genetically isolated more recently than cave populations. In general, all three methods to estimate gene flow provided Nm estimates of the same magnitude.     

Partitioning heterozygosity in subdivided populations: Some misuses of Nei's decomposition and an alternative probabilistic approach

Nei's decomposition of total expected heterozygosity in subdivided populations into within‐ and between‐subpopulation components, H_S and D_ST, respectively, is a classical tool in the conservation and management of genetic resources. Reviewing why this is not a decomposition into independent terms of within‐ and between‐subpopulation gene diversity, we illustrate how this approach can be misleading because it overemphasizes the within‐subpopulation component compared to Jost's nonadditive decomposition based on gene diversity indices. Using probabilistic partitioning of the total expected heterozygosity into independent within‐ and between‐subpopulation contributions, we show that the contribution of the within‐subpopulation expected heterozygosity to the total expected heterozygosity is not H_S, as suggested by Nei's decomposition, but H_S/s, with s being the number of subpopulations. Finally, we compare three possible approaches of decomposing total heterozygosity in subdivided populations (i.e., Nei's decomposition, Jost's approach, and probabilistic partitioning) with regard to independence between terms and sensitivity to unequal subpopulation sizes. For the conservation and management of genetic resources, we recommend using probabilistic partitioning and Jost's differentiation parameter rather than Nei's decomposition.     

Conservation Genetics of the Endemic Mexican Heliconia uxpanapensis in the Los Tuxtlas Tropical Rain Forest

Heliconia uxpanapensis (Heliconiaceae) is an outcrossing endemic herb that grows within continuous and fragmented areas of the tropical rain forest of southeast Veracrúz (México). The genetic diversity, population differentiation, and genetic structure of seven populations of the studied species were assessed using inter‐simple sequence repeat) markers. Population differentiation was moderately high (F_ST range: 0.18–0.22) and indirect estimates of gene flow were rather low (Nm=0.65–0.83). Analysis of molecular variance indicated that the populations explained 22.2 percent of the variation, while individuals within the populations accounted for 77.8 percent. The similar and high level of genetic diversity found within populations of the continuous and fragmented forest suggests that H. uxpanapensis has not suffered yet the expected negative effect of fragmentation. Genetic structure analyses indicated the presence of fewer genetic clusters (K=4) than populations (N=7). Three of the four fragmented forest populations were assigned each to one of the clusters found within the continuous forest, suggesting the absence of a negative fragmentation effect on the amount and distribution of genetic variation. Given the significant genetic structure combined with high genetic diversity and low levels of gene flow, theoretical simulations indicated that H. uxpanapensis might be highly susceptible to changes in the mating system, which promotes inbreeding within fragmented populations. Thus, future conservation efforts in this species should be directed to ensure that levels of gene flow among populations are sufficient to prevent an increment in the magnitude of inbreeding within fragments.     

RECENT EVOLUTION AND DIVERGENCE AMONG POPULATIONS OF A RARE MEXICAN ENDEMIC,CHIHUAHUA SPRUCE,FOLLOWING HOLOCENE CLIMATIC WARMING

Fragmentation and reduction in population size are expected to reduce genetic diversity. However, examples from natural populations of forest trees are scarce. The range of Chihuahua spruce retreated northward and fragmented coincident with the warming climate that marked the early Holocene. The isolated populations vary from 15 to 2441 trees, which provided an opportunity to test whether census number is a good predictor of genetic diversity. Mean expected heterozygosity, H_e, based on 24 loci in 16 enzyme systems, was 0.093 for 10 sampled populations, which is within the range reported for conifers. However, estimates varied more than twofold among populations and H_e was closely related to the logarithm of the number of mature trees in the population (r_He,N = 0.93). Diversity among populations, F_ST, was 24.8% of the total diversity, which is higher than that observed in almost all conifer species studied. Nei's genetic distance, D, was not related to geographic distance between populations, and D? was 0.033, which is higher than estimates for most wide-ranging species. Most populations had excess homozygosity and the fixation index, F_IS, was higher than that reported for all but one species of conifer. Nm, the number of migrants per generation, was 0.43 to 0.76, depending on estimation procedure, and is the smallest observed in conifers. The data suggest that populations of Chihuahua spruce have differentiated by drift and that they are effectively isolated. The results illustrate how a combination of paleontological observation and molecular markers can be used to illuminate recent evolutionary events. Multilocus estimates of outcrossing for two small populations were zero (complete selfing) and 0.153, respectively, which are in striking contrast to the near complete outcrossing observed in most conifers. The high fixation index and a high proportion of empty seeds (45%) suggest that inbreeding may be a serious problem for conservation of Chihuahua spruce.     

Genetic Diversity and Population Structure of Alnus hirsuta (Betulaceae) in Korea

Alnus hirsuta in Korea was measured to estimate the amount and pattern of genetic diversity and population structure. The mean genetic diversity within populations was 0.166. Korean alder populations have slightly high levels of genetic diversity compared to those of two Canadian alder species. The genetic differentiation among populations accounted for 9% of the total variation. The rate of gene flow was estimated high (Nm=2.63). Analysis of inbreeding coefficient, calculated for all polymorphic loci in each population, showed a substantial heterozygote deficiency relative to Hardy-Weinberg expectations. The mean G _ST value of A. hirsuta in Korea was 0.087. The low value of G _ST in this species, reflecting little spatial genetic differentiation, may indicate extensive gene flow. A relationship between the mean heterozygosity and annual rainfall showed a positive relationship (r ²=0.54, F=4.67). Received 8 August 1998/ Accepted in revised form 7 July 1999     

Genetic diversity and population structure in Elephantopus scaber (Asteraceae) from South China as revealed by ISSR markers

Abstract

We used inter-simple sequence repeat (ISSR) markers to investigate genetic variation in eight natural populations of Elephantopus scaber from South China, including Guangdong, Hainan and Hong Kong. Eleven primers produced 247 bands across all 184 individuals, of which 243 (98.4%) were polymorphic. The average genetic diversity at the species and population levels was estimated to be 0.283 and 0.103, respectively, using mean expected heterozygosity. The average gene differentiation (F _ST) among populations was 0.725. AMOVA analysis showed that the partition of molecular variation between and within populations was 72.5% and 27.5%, respectively. The effective number of migrants among populations based on the F _ST was relatively low (N _m = 0.095). Cluster analysis based on Nei's genetic distance and the neighbour-joining method revealed the genetic relationships among the populations of E. scaber. The Mantel test indicated that there was no significant correlation between population genetic and geographic distances. The results obtained from the AMOVA analysis, the cluster analysis, and the Mantel test all suggested that fragmented local environments and human disturbance might play important roles in shaping the population structure of E. scaber.     

EVIDENCE FOR LONG-DISTANCE POLLEN DISPERSAL IN MILKWEEDS (ASCLEPIAS EXALTATA)

We investigated pollen-mediated gene flow and interspecific matings in natural populations of poke milkweed, Asclepias exaltata. Genetic data from 16 polymorphic isozymes allowed unambiguous identification of the diploid paternal genotype for 225 singly sired fruits collected from six populations in Shenandoah National Park, Virginia. Paternity analysis of progeny arrays revealed that 29%–50% (39.2%, mean) of the seeds produced in these populations were sired by plants located outside each target population. Variation among populations appears to be related to isolation distance (Kendall's τ = ?0.69, N = 6, P > 0.1), although the negative correlation was statistically significant only when the results from a previous study of A. exaltata were also included in the analysis (Kendall's τ = ?0.78, N = 7, P < 0.05). The coupling of standard paternity exclusion analysis on individual seeds (12 seeds/fruit) with estimation of cryptic gene flow from Monte Carlo simulations accounted for only 65% of the gene flow detected using the progeny-array analysis. These results suggest that standard paternity exclusion, incorporating cryptic gene flow, will inherently underestimate actual gene flow rates when the number of paternal parents is smaller than the number of seeds per fruit (i.e., matings are correlated). Indirect estimates of the number of migrants per generation (Nm ≈ 2.3) obtained from Nei's genetic diversity statistic (G_ST) are much smaller than realized gene flow measured in 1990 (Nm = 9.4, progeny-array method). In addition, interspecific hybridization with common milkweed, Asclepias syriaca, via long-distance pollen dispersal was detected in two fruits (0.8%). Thus, pollen-mediated gene flow and infrequent interspecific matings provide mechanisms to lower genetic differentiation among populations to maintain novel, low-frequency alleles within populations of A. exaltata.     

Low Levels of Genetic Diversity within Populations of Hosta clausa (Liliaceae)

Abstract Genetic diversity of Korean populations in Hosta clausa was investigated using starch gel electrophoresis. Hosta clausa is widespread, grows only along streamsides, and has both sexual and asexual reproduction. Populations of the species are small and isolated. Thirty-two percent of the loci examined were polymorphic, and mean genetic diversity within populations (He_p=0.082) was lower than mean estimates for species with very similar life history characteristics (0.131), particularly for its congener H. yingeri (0.250). The mean number of multilocus genotypes per population was 8.7, and genotypic diversity index (D_G) was 0.84. Significant differences in allele frequencies among populations were found in all seven polymorphic loci (P < 0.001). About one-fifth of the total allozyme variation was among populations (G_ST=0.192). Indirect estimate of the number of migrants per generation (Nm=0.48, calculated from mean G_ST) and nine private alleles found indicate that gene movement among populations was low. The low levels of genetic diversity within populations and the relatively high levels of genetic diversity among populations suggest that strong moist habitat preferences, clonal reproduction, low level of gene flow among populations, genetic drift, and historical events may have played roles in the genetic structuring of the species.     

Population structure and genetic diversity of Stipa grandis P. Smirn,a dominant species in the typical steppe of northern China

Random amplified polymorphic DNA (RAPD) markers were used to characterize genetic heterogeneity within and among five populations of Stipa grandis in the Xilingol Plateau. Estimates of the percentage of polymorphic bands, Shannon's diversity information index and Nei's gene diversity index were comparatively high in the five populations, and the Population GSM was found to have the highest genetic diversity among all populations. An analysis of molecular variance indicated that the majority of variation existed within populations (74.12%), and that there was significant differentiation among populations (Φ_ST = 25.88%, P < 0.001). Genetic distance (Φ_ST) ranged from 0.198 to 0.310 and the differentiation between pair-wise populations was significant when individual pairs of populations were compared. Based on the Φ_ST values, gene flow (Nm) was estimated and was found to vary from 0.556 to 1.013 between pair-wise populations and 0.7412 among populations. The results of UPGMA cluster analysis and nonmetric multi-dimensional scaling analysis indicated that most variation occurred within populations and that genetic differentiation had happened between populations. These findings are important for a better understanding of the adaptive strategy of S. grandis in northern China and will be useful for conservation managers to work out an effective strategy to protect this important species.     

Genetic diversity and gene flow estimates among three populations of Botryodiplodia theobromae causing die-back and bark canker of pear in Punjab

Three populations of Botryodiplodia theobromae causing die-back and bark canker of pear in Punjab were analysed to know about the genetic diversity, gene flow, heterogeneity and the probable rate of spread of races capable of overcoming the resistance present in elite cultivars. There was no relationship between the morphologically similar isolates and their pathogenic behaviour. Majority of the isolates of B. theobromae within and among the populations produced lesions of 1.9–7.2 × 0.8–3.1 cm size on detached pear twigs cv. Punjab Beauty. Incubation period and per cent infection also varied within and among the three populations of the pathogen. The genetic diversity was calculated on the basis of allele frequencies of nine simple sequence repeat (SSR) markers using Nei's genetic diversity formulae. Allele frequencies (X_ij ) varied significantly among the three populations ranging from 0.0 to 1.0. The mean genetic diversities within population (H _S) also varied in all the locations ranging from 0.18 to 0.36 indicating a high genetic diversity within the population. The total genetic diversity across all the populations (H _T) ranged between 0.1 and 0.5 with a mean of 0.36, and differed significantly from the mean H _S (0.25). Diversity indices of SSR loci varied from low (H _S < 0.1) to high (H _S > 0.4) across all the populations (G _ST) of B. theobromae in Punjab which were consistent over the presumed SSR loci with a mean G _ST of 0.29. The lower G _ST values of 0.13, 0.10, 0.11 and 0.13 were observed at LAS15-16, LAS27-28, BOT17-18 and BOT35-36 loci, respectively, showing high genetic diversity among all the isolates. However, at BOT19-20 locus, the G _ST value observed was 0.72 thereby indicating low diversity in the population at this locus. Out of 25 loci, 8 loci showed the gene flow (Nm) < 1 indicating a high genetic differentiation within the population and the remaining 6 loci showed the Nm > 1 indicating the frequent existence of gene flow across the populations of B. theobromae. Pairwise comparison (G _ST) values among all the loci were ranging from 0.18 to 0.19, which indicate a low genetic differentiation among the populations of B. theobromae. The high genetic diversity (H _S) within the population was observed in the present study suggesting that B. theobromae possess high variability in Punjab. Keeping this in view, new races would be expected soon outside the state of origin, as naturally occurring gene flow is likely to be increased by the human activity for comprehensive cultivation of pear in the near future. Therefore, it is difficult to predict the durability of resistant sources in Punjab, which in turn emphasises the identification and introgression of R genes into commercial cultivars.     

Shape variation in surface and cave populations of the armoured catfishes Ancistrus(Siluriformes: Loricariidae) from the São Domingos karst area, upper Tocantins River, Brazil

Body shape of four distinct populations of Ancistrus cryptophthalmus from different caves in the São Domingos karst area and the local epigean (surface) Ancistrus species were compared using geometric morphometrics. Angélica and Bezerra catfishes were closer to each other and successively to the studied sample of epigean catfishes than to Passa Três and São Vicente I catfishes. Greater similarity between catfishes from the Angélica‐Bezerra cave system to epigean catfishes than to other cave catfishes may represent a plesiomorphic feature. On the other hand, the present analyses allowed the distinction between Passa Três and São Vicente I catfishes, which inhabited the same cave system. Topographic isolation due to the presence of several waterfalls interposed between the stream reaches where these catfishes live may explain such morphological differentiation. Also, the presence of a waterfall downstream of the reach where the Angélica sample was obtained may have contributed to the partial isolation of these catfishes from those living in Bezerra Cave. Differences in population sizes probably influenced the degrees of morphological differentiation observed among the cave populations. The mosaic distribution of character states indicated that the four populations of A. cryptophthalmus have evolved rather independently, but the continuous variation suggests a recent connection between these populations, perhaps with a limited gene flow. Considering other features such as reduction of eyes and pigmentation, and changes in body shape, a separate species status for the epigean and hypogean Ancistrus species from the São Domingos karst area has been maintained.     

CORRELATION OF PAIRWISE GENETIC AND GEOGRAPHIC DISTANCE MEASURES: INFERRING THE RELATIVE INFLUENCES OF GENE FLOW AND DRIFT ON THE DISTRIBUTION OF GENETIC VARIABILITY

Attempts to relate estimates of regional F_ST to gene flow and drift via Wright's (1931) equation F_ST ≈ 1/ (4Nm + 1) are often inappropriate because most natural sets of populations probably are not at equilibrium (McCauley 1993), as assumed by the island model upon which the equation is based, or ineffective because the influences of gene flow and drift are confounded in the product Nm. Evaluations of the association between genetic (F_ST) and geographic distances separating all pairwise populations combinations in a region allows one to test for regional equilibrium, to evaluate the relative influences of gene flow and drift on population structure both within and between regions, and to visualize the behavior of the association across all degrees of geographic separation. Tests of the model using microsatellite data from 51 populations of eastern collared lizards (Crotaphytus collaris collaris) collected from four distinct geographical regions gave results highly consistent with predicted patterns of association based on regional differences in various historical and ecological factors that affect the amount of drift and gene flow. The model provides a prerequisite for and an alternative to regional F_ST analyses, which often simply assume regional equilibrium, thus potentially leading to erroneous and misleading inferences regarding regional population structure.     

Genetic diversity in fragmented populations of the critically endangered spider orchid Caladenia huegelii: implications for conservation

The Orchidaceae is characterised by a diverse range of life histories, reproductive strategies and geographic distribution, reflected in a variety of patterns in the population genetic structure of different species. In this study, the genetic diversity and structure was assessed within and among remnant populations of the critically endangered sexually deceptive orchid, Caladenia huegelii. This species has experienced severe recent habitat loss in a landscape marked by ancient patterns of population fragmentation within the Southwest Australian Floristic Region, a global biodiversity hotspot. Using seven polymorphic microsatellite loci, high levels of within-population diversity (mean alleles/locus = 6.73; mean H _E = 0.690), weak genetic structuring among 13 remnant populations (F _ST = 0.047) and a consistent deficit of heterozygotes from Hardy–Weinberg expectation were found across all populations (mean F _IS = 0.22). Positive inbreeding coefficients are most likely due to Wahlund effects and/or inbreeding effects from highly correlated paternity and typically low fruit set. Indirect estimates of gene flow (Nm = 5.09 using F _ST; Nm = 3.12 using the private alleles method) among populations reflects a historical capacity for gene flow through long distance pollen dispersal by sexually deceived wasp pollinators and/or long range dispersal of dust-like orchid seed. However, current levels of gene flow may be impacted by habitat destruction, fragmentation and reduced population size. A genetically divergent population was identified, which should be a high priority for conservation managers. Very weak genetic differentiation indicates that the movement and mixing of seeds from different populations for reintroduction programs should result in minimal negative genetic effects.     

基于SSR标记的大明松天然群体遗传多样性分析

大明松是广西和贵州特有的高山松类,具有很高的经济价值和生态价值,其自然种群长期没有得到充分的保护和利用,不利于该树种长期稳定发展。为了合理保护和开发利用大明松天然遗传资源,该文利用12个SSR分子标记对大明松3个天然群体进行遗传多样性研究,分析其群体间的遗传分化和基因流,为该物种的保护策略提供参考。研究结果表明:(1)12对引物共检测到37 个等位基因,多态位点百分率为100%。每个位点平均观察等位基因数(Na)为3.08,平均有效等位基因数(Ne)为1.68, 不同位点间有效等位基因数差异较大; 每个位点平均观察杂合度(Ho)为0.35,平均期望杂合度(He)为0.40,平均多态信息含量(PIC)为0.31。(2)3 个群体的Shannon''s多样性指数变化范围为0.48～0.65,Nei''s基因多样度的变化范围为0.27～0.39,与其他近缘种松类相比遗传多样性偏低。群体平均观察杂合度为0.40,平均期望杂合度为0.33,平均有效等位基因数为1.58。群体间基因分化系数(Gst)为0.10,群体间的遗传分化水平较低,大部分变异均存在群体内。群体间的基因流(Nm)为2.74,说明大明松群体间的基因交流比较充分。该研究可为大明松生物多样性保护提供重要参考依据,为科学利用大明松资源打下基础。     

Genetic diversity and structure of natural Pinus tabulaeformis populations in North China using amplified fragment length polymorphism (AFLP)

Chinese pine (Pinus tabulaeformis carr.), endemic to China, is a conifer species with extensive and fragmented distribution in North China. In this study, the genetic diversity and structure of 20 natural populations of this species were investigated using amplified fragment length polymorphism (AFLP) markers. A total of 445 fragments were revealed with 8 pairs of primers, 379 (85.17%) of which were polymorphic. A moderate level of genetic diversity was detected at the species level (Shannon's information index I = 0.356, Nei's gene diversity H_E = 0.271) and at the population level (I = 0.219, H_E = 0.206). Most of genetic variation was within populations while a considerable level of genetic differentiation was detected (G_ST = 0.352, Ф_ST = 0.304). The high differentiation could be attributed to the complex and fragmented habitats, and a limited gene flow among populations (N_m = 0.572). The Mantel test indicated that there was significant correlation (r = 0.455, P < 0.001) between Nei's genetic distance and geographical distance among all the populations. The results suggested that proper countermeasures should be taken to prevent the habitat further deterioration and maintain the genetic diversity of this species.     

Nontroglobitic Fishes in Bruffey-Hills Creek Cave, West Virginia, and other Caves Worldwide

Six species of fishes were tagged and released in September and November 1995 and on five dates between November 1998 and October 1999 inside Bruffey-Hills Creek Cave. Most of the tagged fishes were creek chub, Semotilus atromaculatus, and green sunfish, Lepomis cyanellus. The overall recapture rate was 2.6% as only three of 117 fishes were recaptured. Forty-nine days was the longest time of residence by two L. cyanellus and one S. atromaculatus, and movement of 83.4 m was observed only for the creek chub. Tag loss was confirmed as one factor in the low recapture rate. Nine species of fishes were collected in the cave, including Phoxinus oreas and Pimephales promelas, two species never collected in a cave. Most of the fishes were pigmented normally, but many creek chubs were depigmented and appeared white or pigmentless when first observed in the cave stream. Four species, Phoxinus oreas, Pimephales promelas, Ameiurus nebulosus, and Lepomis macrochirus, were collected for the first time in Bruffey-Hills Creek Cave and in the Bruffey and Hills creeks drainage. Although data from this study did not shed light on residence time of fishes in the cave, the consistent occurrence of epigean fishes in this cave was shown. A list of epigean fishes from caves worldwide was included along with a discussion of aspects of the ecology of epigean fishes in caves and of evolution of troglobitic fishes.     

Genetic differentiation among populations ofArabis serrata (Brassicaceae) along its geographic distribution

Levels and distribution of genetic variation were investigated in ten populations of the perennialArabis serrata distributed along a latitudinal gradient throughout Japan. Populations of this endemic species occupy predominantly three types of habitats: limestone and derived soils, volcanic and disturbed sites. Previous studies showed that plants ofA. serrata are differentiated in morphological and ecological traits under both natural conditions and common garden experiments suggesting genetic differentiation among populations. To assess the degree of genetic differentiation under different habitats ofA. serrata populations, we analyzed the isozyme genetic structure. Ten populations, located in mountains of central and northern Honshu and Hokkaido, were analyzed by starch gel enzyme electrophoresis. Fourteen loci of eight enzymes were resolved and six loci were monomorphic for all the populations. Populations sampled maintain low levels of genetic variation (P=0.16;H=0.05;A=1.16) compared to that maintained by other outcrossing seed plants. In some cases, few or no heterozygous individuals were detected, and consequently, mean observed heterozygosity was zero or near zero. Six (29%) of the fixation indices,F, estimated deviated significantly from Hardy Weinberg genotypic expectations indicating a deficiency of heterozygotes in most of the cases. The mean genetic identity (Nei'sI) between population pairs was 0.852 and indicates a moderate level of genetic differentiation among populations.Arabis serrata has most of its genetic variation distributed among rather than within populations. The among-population component of the total genetic diversity (G _ST mean value) was 0.416, indicating genetic differentiation between populations. There groups of populations were recognized in an unrooted tree generated by the Neighbor-Joining method. These results suggest groups of populations differentiated regionally. Estimates of interpopulational gene flow (Nm) were very variable (range 0.049–3.718) with a meanNm=1.203 for all populations.     

The population genetic diversity and pattern of Pteroceltis tatarinowii,a relic tree endemic to China,inferred from SSR markers

Pteroceltis tatarinowii (Cannabaceae), a relic tree endemic to China, is mainly distributed in limestone mountains and has a wide geographical range. In this study, 12 microsatellite primer pairs were assayed to analyse the genetic pattern and gene flow among 461 individuals sampled from 23 wild populations of P. tatarinowii. A high level of genetic diversity was detected based on high values of total alleles (159), the number of alleles (N_A = 6.373), expected heterozygosity (H_E = 0.696) and observed heterozygosity (H_O = 0.679). The high genetic diversity in this species may be attributed to its long‐life history, wide geographical distribution and wind dispersal. Only low genetic differentiation (G_ST = 0.137, F_ST = 0.138) was found among populations. Gene flow (migrants per generation, N_m) was estimated to be 1.56. This moderate level of gene flow possibly decrease interpopulation differentiation by buffering against genetic drift and improving gene exchange. However, spatial genetic structure was detected throughou the sampled range of the species (r = 0.311, p < 0.05) as well as in southern China (r = 0.453, p < 0.05), and may be related to terrain heterogeneity and the demographic history of P. tatarinowii. The east‐west high mountains of southern China might serve as physical barriers to seed and pollen flow. The isolation and local adaptation of different refugia may further limit gene flow. In addition, geographically remote populations might fail to effectively disperse pollen and seeds. Based on the above‐mentioned results, some suggestions for the conservation of the species are presented.